Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a transitional graphical user interface, showing my new design, in accordance with a first embodiment and showing a first image thereof.

FIG. 2 is a front view of a second image thereof.

FIG. 3 is a front view of a third image thereof.

FIG. 4 is a front view of a fourth image thereof.

FIG. 5 is a front view of a display screen or portion thereof with a transitional graphical user interface, showing our new design, in accordance with a second embodiment and showing a first image thereof.

FIG. 6 is a front view of a second image thereof.

FIG. 7 is a front view of a third image thereof; and,

FIG. 8 is a front view of a fourth image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-4 or between the images shown in FIGS. 5-8. The process or period in which one image transitions to another image forms no part of the claimed design.

Subject matter shown in broken lines, including the display screen and the remainder of the transitional graphical user interface, is included for the purpose of illustrating environmental structure, and the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 